The present invention relates generally to internal combustion engines. More particularly, the present invention relates to manifolds or other passageways for directing fluids within internal combustion engines.
Internal combustion engines are commonly used to provide power for lawn care and gardening implements such as rototillers, lawnmowers, edgers, and the like. These internal combustion engines generally include a carburetor that feeds an air/fuel mixture to one or more cylinders.
It is sometimes desirable to position the carburetor or other air/fuel mixing device on one side of the engine, while the cylinder intake valve(s) is located on the opposite side. In this type of arrangement, an intake crossover manifold or tube is employed to provide a flow path for the air/fuel mixture. To provide the best air/fuel mixture by reducing turbulent fluid flow, it is desirable to provide the smoothest flow path possible between the carburetor and the cylinder intake. Thus, straight tubes or tubes with smooth bends are preferred over typical tubes with relatively sharp or small inner radius bends.
Some prior art tubes were manufactured out of metal. These metal tubes were typically manufactured from two separate pieces. Specifically, a tube portion attached to a die cast portion. However, these tubes included a sharp inner radius and were relatively expensive to manufacture.
Other tubes were manufactured from thermoplastic materials. However, the high temperatures generated by the engine can soften the thermoplastic. This softening necessitates the use of more rigid tubes that include shoulder inserts, stiffening ribs, or other stiffening features. In addition, an o-ring or gasket must be used to assure a seal and to thermally insulate the tube from the hottest engine components. Other items, such as metal threaded inserts may also be required, thereby increasing the cost of thermoplastic tubes. These additional costs increase the cost of the engine.
Tubes having the desired inner radius can be manufactured using multi-piece or rotating cores. However, the methods of manufacture used are costly. In addition, the thermoset plastic tends to cause wear and sticking problems when used in conjunction with rotating cores. This makes it difficult to form a smooth-walled part including the desired inner radius using thermoset plastics.
FIG. 1 illustrates one prior art tube 1 in section. As can be seen, the inner corner of the tube 2 is not radiused. This sharp corner creates turbulence and other flow losses that are undesirable.